US2885327A - Process of coking solid carbonizable material - Google Patents

Description

y 1959 P. M. YAVORSKY 2,885,327

PROCESS OF COKING SOLID CARBONIZABLE MATERIAL Filed May 14, 1956 AAA/l COKE LAYER E G R A H C COAL LAYER ORIGINAL coma LAYER PLASTIC LAYER UNCOKED COAL CHARGE COKE PORTION OF COAL CHARGE INVENTOR.

PAU L M. YAVORSKY Ii 1 vtiilll\ KK QA ATTORNEY PROCESS OF COKING SOLID MATERIAL Application May 14, 1956, Serial No. 584,498 5 Claims. (Cl. 20229) The present invention relates to the coking of solid combustible carbonaceous materials and, more particularly, to an improved method for increasing the rate of production of coke from bituminous coal.

Conventional high temperature coking of bituminous coal is an inherently slow batch heating operation. The numerous attempts in the past to increase the coking rate of commercial coke ovens have met with but limited success. There have been suggestions that hot gases be introduced through perforations in the oven walls, and carried throughout the coking mass via granular layers or channels, tubes and various other means. These methods have no application today since economics dictate that the gaseous products of the coking process be kept undiluted. It was therefore necessary to look to other means to increase the coking rate. The present invention increases the coking rate, not by such attempts to employ convection, but rather by improving conduction through the coking mass itself.

In a commercial coke oven today, coal is charged between the substantially parallel vertical walls of a slot oven. The coal is dumped into the oven through a number of openings in the oven roof, which are sealed. Each individual oven within a battery is heated by conduction through the oven Walls from flues located on the two long sides of the slot oven.

The coal which is in contact with the hot oven walls becomes soft and forms a thin plastic layer adjacent to the heating surfaces. This plastic layer, which comprises the actual coking zone, advances away from the heating surface and into the charge leaving coke in its wake. I

There is a sharp temperature gradient across the thin plastic layer. Its outer or wall side will vary from the inner wall temperature of the oven (circa 1000" C.) to about 500 0, depending on the distance it has travelled from the wall. The temperature of the materials within the plastic layer will range between 500 C. and 350 C. Despite the extremely large amount of heat applied to the charge, very little of it is transferred beyond the plastic layer because of the poor conductivity of coal. The uncarbonized coal ahead of the advancing plastic layer remains relatively cool. The center of the charge maintains a constant temperature of about 100 C.-115 C. until the plastic layer reaches it. As the plastic layer advances, the applied heat must reach it by passing through the oven walls and thence through the product coke. The rate of advance is about /z-in :h per hour; hence, in a conventional 18-inch wide oven, where coking layers advance from two opposite walls, about 18 hours are required to coke one charge. Even those coke ovens which have adopted alloy-steel or Carborundurn linings in an attempt to accelerate the process and increase coke production are limited in throughput by the rate of heat transfer through the charge.

The prior art shows belief that coal and coke possess essentially the same thermal conductivity, and in fact, some prior art indicates a belief that coke possesses a rates Patent C 2,885,327 Patented May 5, 1959 lower thermal conductivity than does coal. I have found, however, that the thermal conductivity of coke is many fold greater than that of coal (perhaps 40 times larger) and have, according to the present invention, applied this discovery to an improved method for operating conventional coke ovens.

I propose to charge a conventional coke oven with alternate layers of coal and finely divided coke (circa %-inch mesh). The more highly conductive layers of coke heat up rapidly and become in efiect horizontal thermal walls or heating surfaces interspersed with the coal charge. The coal in contact with a hot coke layer softens and forms a plastic layer as does the coal in contact with a hot wall of the oven. The plastic layers thus formed above and below each hot coke layer advance vertically upward and downward into the respective adjacent coal layers.

It is readily seen that my invention has greatly increased the area of the effective heating surfaces which can produce and sustain plastic layers. Coking progresses in four rather than two directions. In effect my invention has created a number of small coking zones within the one large oven. As a result of the increased area of the plastic coking layer, the amount of coke being produced at any given time is substantially increased.

It is apparent that an existing coke oven will receive less coal during each charging cycle according to my invention since a significant volume of the charge comprises recycled coke. However, the increased heat trans fer is to striking that the coking time for a layered charge in a conventional by-products oven may be reduced by 50 percent or more. The net result is a significant increase in the coal throughput of the oven.

Since the coke layers remove heat more rapidly from the inner surface of the oven walls than does a conventional oven charge, it is possible to increase the amount of heat externally suplied to the walls without raising the temperature of the inner surface of the wall. If the inner wall temperature is so maintained, the plastic layer will advance at the same rate as it would in a conventionally charged oven. Thus despite the increase in overall coking rate, the actual rate of applying heat to any individual particle of coal within the oven charge is not altered by my invention. 1

Since coke quality is dependent upon the coking rate of a given particle, the freshly produced coke in a layered charge is of comparable quality to that obtained by conventional charging.

Another incidental improvement of my invention is to alleviate the pressure problems inherent in the coking of bituminous coal. As the plastic layers advance toward each other in a conventionally charged coke oven, there is a tendency for the edges to advance more rapidly than the rest of the surface. When these edges meet, an envelope is formed which confines the gases evolved on the inner side of each impermeable plastic layer. The gas pressure within the envelope increases until the envelope ruptures. If the average pressure on the oven walls exceeds two pounds per square inch, it is likely that damage to the oven will result.

When coke ovens are operated according to the present invention, the large envelope is replaced by a number of smaller ones and thus the force exerted on the oven walls is decreased. These small envelopes are hon'zorn tally elongated and thus exert most of the pressure vertically. Hence, most of the expansion will likewise be vertical. The gas space in the coke oven above the charge allows for such movement. Heating and conse quent movement across the charge will be unequal. This will have a tendency to rupture the small plastic envelopes and prevent excessive pressure accumulations.

. By in the present invention it may be possible to coke highly 3 caking coals which heretofore have been rejected as coke oven feeds.

The principal object of this invention is to increase the amount of coke which can be produced from conventional coke ovens per unit of time.

A more specific object of the invention is to Increase the total amount of coal which can be coked in a conventional coke oven per unit of time without changing the heating rate of any given particle of the coal charge.

A further object of the invention is to decrease the period of time required for the completion of heat transfer between the externally heated walls of the vessel and the center of the coal charge.

Another object of the invention is to provide a plurality of heating surfaces within the oven charge itself in addition to the heating surfaces furnished by the walls of the oven.

A still further object is to permit more heat to be applied externally to the vessel without changing the inner wall temperature of the oven.

Another object of the invention is to alleviate the pres sure problems normally encountered in the coking of coal in a coke oven.

These objects are accomplished according to the present invention by charging the coke oven with alternate layers of coal and finely divided coke and then externally heating the oven and carrying out the coking process in the conventional manner.

A conventional coke oven as referred to in the present specification is a by-product oven having a coking chamber approximately 40 feet long, 14 feet high and 18 inches wide. When charged to a height of 12 feet, the chamber holds 18 tons of coal having a density of 50 pounds per cubic foot. Such an oven will produce about 13 tons of coke per charge after an 18 hour residence time. The flue temperature is normally maintained at about 1300 C. while the temperature of the inner surface of the oven wall is about 1000 C.

In the accompanying drawings forming a part of the specification:

Figure 1 is a fragmental, cross-section view in end elevation of two conventional coke oven chambers and their horizontal lines and cross overs taken at right angles to the horizontal extension of the individual ovens, and longitudinal to the entire coke oven battery. The draw ing shows one oven as conventionally charged with coal only, and another oven charged with layers of coke and coal in accordance with the present invention.

Figure 2 is a fragmentary, cross-sectional view of a coal layer situated between two layers of coke in a conventional oven and, taken at right angles to the horizontal extension of the oven, showing the progressive advance of the plastic coking zone into the coal layer.

Referring again to the drawings, Figure 1 shows two oven chambers; chamber 1 is represented as just having been charged with a conventional coal charge, and oven chamber 3 is represented as just having been charged with alternate layers of coal 5 and coke 7. The chambers are bounded by two longitudinally extending flued masonry walls 9, an oven sole 11, and a masonry roof 13. Each oven chamber is separated from the next oven chamber in the battery by a flue 15. The ovens are supplied with regenerators 17, air ports 23, waste heat ports 19 and fuel gas burner nozzles 21.

According to the well known process of heating reversible regenerative coke ovens, air flows through the checkerwork in the regenerator 17 and passes therefrom through air ports 23 and into on lines 15 for combustion therein with fuel gas entering through fuel gas burner nozzle 21. The burning gases pass through crossover ducts 25 and descend through off flues 15 on the opposite side of the oven chamber. At periodic intervals the heating system is reversed and the present on flue wherein the gas is burned, becomes an off fiue and receives the hot gases of combustion from the burning of fuel gas in the present otf" flue. The gases then flow through waste heat ports 19 and enter another set of regenerators 17. There thewaste heat is utilized to preheat the checkerbrick contained therein, preparatory to reversing the system.

Figure 2 illustrates in detail the layers of coke and coal shown in oven chamber 3 of Figure 1 to indicate the actual coking process in the present invention. The oven walls are indicated by 27 while the single heavy line 29 represents the advancing plastic layer. 31 is the original coke layer as charged to the oven; 33 is the coke formed by the advance of the plastic layer; 35 is the remaining uncarbonized coal. As indicated by arrows 37, the plastic layer 29 advances not only horizontally from the walls 27, but vertically from the layers of coke 31 above and below the coal charge. To use the present invention to advantage, the coal layers should not be as thick as the oven is wide. Thus the vertical distance which the plastic layer must advance is less than the horizontal distance which must ordinarily be traversed.

In order to decrease the length of time required to coke a given amount of bituminous coal, it is necessary to increase the rate at which heat is supplied to the coking mass. This can be accomplished by raising the flue temperature and thus the outer wall temperature of the oven. In a conventionally charged oven, the inner wall temperature would likewise increase since the coking mass cannot readily utilize the additional heat. The combination of more heat and a higher wall temperature results in increasing the rate at which the plastic coking layer advances into the charge, which in turn is deleterious to coke quality. By employing the present invention, however, it is possible to supply more heat to the Walls without changing the inner wall temperature since the more highly conductive coke layers rapidly conduct the excess heat away from the walls and into the center of the charge. As a result the rate of plastic layer advance is unaltered and coke quality is maintained when the present invention is utilized.

It should be particularly noted that when my invention is employed, the limiting factor on the net throughput of coal is the ability of the oven walls to supply heat to the charge. As more heat is made available, I simply use more coke layers to distribute the heat through the coking mass.

Since the individual coke layers need be only thick enough to constitute intact layers across the oven, I prefer to use coke layers of about one-inch thickness. The thickness of the coke layers may be varied to meet loading and operating conditions at any specific installation, but it must be remembered that the use of unnecessarily thick coke layers needlessly decreases the coal throughput of the oven.

The heat flow through an oven wall is directly proportional to the temperature difference (AT) through the wall. By raising the outer wall temperature of a conventional oven from its normal value of about 1300 C. to a higher value of about 1600 C. (maxim-um temperature which silica bricks can tolerate) while maintaining the inner wall temperature at its conventional value of about 1000 C., it is possible to double the heat flow into the oven.

AT 1300=1300l000=300 C. AT 1600=16001000=600 C.

Thus, it is apparent that where the temperature difference through the wall is doubled, so too is the heat flow through the Wall. With heat flow doubled, the coking time for a coal charge can be halved. This is more readily apparent when it is remembered that a layered charge contains a percentage of coke which needs no heat to carbonize it.

Alternate nine-inch layers of coal and one-inch layers of coke, ,when charged into a conventional coke oven operating with an outer wall temperature of 1600 C. will maintain the inner wall temperature of 1000 C. The coking time for the charge is decreased from the 18 hours normally required in present oven operations down to 9 hours, with a throughput of 16.2 tons of coal per charge. Ignoring the relatively short period of time required to discharge product coke and recharge the emptied oven, a net throughput of about 43 tons of coal per day can be achieved in contrast to a net throughput of 25 tons of coal per day if the same oven were conventionally charged and operated.

If alternate 10.8 inch layers of coal and one-inch layer of coke are charged into a conventional oven operated with an outer wall temperature of 1500" C., the coking time is 10.8 hours per charge. The net throughput will be 16.5 tons of coal per charge or 36.6 tons of coal per day.

When alternate 13.5 inch layers of coal and one-inch layers of coke are charged into an oven operating with an outer wall temperature of 1400 C., the coking time is reduced to 13.5 hours and the net throughput will be 30 tons of coal per day.

The following Table I illustrates the net coal throughput of a coke oven which can be obtained by alternating one-inch thick coke layers with coal layers having thicknesses there listed, under coking conditions unlimited by the rate of heat applied to the coking mass. The use of more highly conductive oven linings capable of withstanding higher temperatures would relax the limitations on heating rates inherent in existing coke ovens. Silicon carbide oven linings, for example, should permit greatly increased heating rates.

Table 1 Net Throughput of coal (tons/day) Time For Charge 1 (hours) Coal Layer Thickness (Inches) coke layer (All coal) 24 Meemcnooo 1 Calculated data ignores the period required for discharging product coke and recharging the emptied oven.

2 The heating limitations of existing silica walled ovens limits their maximum throughput to 43 tons of coal per day.

The data in Table I were calculated by the following method:

Coal layer thickness Plastic layer velocity X 2 vertically advancing layers Coal layer thickness N2? Th l"1()l% gput Coal layer thicknessx 18 ton oven capacity g +eoke layer thickness Net throughput per charge Net Throu h ut of Coal i z Coking time per charge The present invention would be of advantage in the operation of a continuous coking process whereby a vertical indirectly heated oven is continuously charged from above with alternate layers of coal and coke, and the product coke is continuously withdrawn from the bottom of the oven. A portion of the hot coke withdrawn from the bottom of the oven can be recycled to provide a hot feed coke for subsequent alternate layers.

The alternate coke and coal layers of the present invention need not be horizontal as illustrated. It is suificient that the coke layers provide a heat transfer route from the hot oven wall to the interior of the oven charge. Although a coke layer which is not continuous from oven wall to oven wall will not give rise to the small envelopes herein described, and will not provide optimum Coking Time X 24 hours per day heat transfer, the improved heat transfer properties will increase the coke yield of the oven. Thus, it is apparent that the invention is not one of critical limitations and may be readily adapted to various types of coke ovens under varying economic conditions.

According to the provisions of the patent statutes, I have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of coking coal which comprises charging an indirectly heated oven with alternate layers of coal and layers of a solid material having a higher thermal conductivity than that of the coal, said coal layers having a depth which is less than the width of said oven, and then externally applying heat to the walls of said oven whereby coke is formed and gases ,are evolved, the evolved gases being led off through the formed hot coke.

2. The method of coking coal which comprises charging an imperforate walled indirectly heated oven with alternate layers of coal and layers of a solid material having a higher thermal conductivity than that of the coal, said coal layers having a depth which is less than the width of said even, and then externally applying heat to the walls of said oven whereby coke is formed and gases are evolved, the evolved gases being led off through the formed but coke.

3. The method of coking coal which comprises charging an imperforate walled indirectly heated oven with alternate layers of coal and coke, said coal layers having a depth which is less than the width of said oven, and then externally applying heat to the walls of said oven whereby coke is formed and gases are evolved, the evolved gases being led off through the formed hot coke.

4. The method of continuously coking coal which consists of charging an indirectly heated oven with alternate layers of coal and coke, said coal layers having a depth which is less than the width of said oven, externally applying heat to the walls of said oven, whereby coke is formed and gases are evolved, subsequently withdrawing the coked product from the bottom of the oven and returning a portion of said product to the top of said oven to provide a feed coke for subsequent alternate layers, the evolved gases being led off through the formed but coke.

5. The method of coking coal which comprises charging an imperforate walled indirectly heated oven with alternate layers of coal and coke, said coal layers having a depth which is less than the width of said oven, and heating the outer side of the walls to a flue temperature which results in advancement of the plastic layer through the coal at a rate substantially equivalent to that occurring in a similar even having a substantially lower flue temperature and containing a charge consisting of coal, whereby coke is formed and gases are evolved, the evolved gases being led off through the formed hot coke.

References Cited in the file of this patent UNITED STATES PATENTS 1,268,628 Rusby et a1. June 4, 1918 2,721,168 Kimbenlin et al Oct. 18, 1955 FOREIGN PATENTS 9,292 Great Britain Nov. 21, 1912 441,029 Great Britain Jan. 10, 1936 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2, 885, 327

Paul Mn Yavorsky It is hereby certified th of the above numbered patent Column 2, line 11, for "with "to striking" read so striking Signed and sealed this 29th SEAL) Attest:

KARL Ha AXLINE Attesting Officer at error appears in the-printed specification requiring correction and that the said Letters Patent should read as corrected below.

May 5, 1959 the" read Within the line 30, for line 3'7, for "suplied read su pplied a day of September 1959.

ROBERT C. WATSON Commissioner of Patents

Claims (1)

1. THE METHOD OF COKING COAL WHICH COMPRISES CHARGING AN INDIRECTLY HEATED OVEN WITH ALTERNATE LAYERS OF COAL AND LAYERS OF A SOLID MATERIAL HAVING A HIGHER THERMAL CONDUCTIVITY THAN THAT OF THE COAL, SAID COAL LAYERS HAVING A DEPTH WHICH IS LESS THAN THE WIDTH OF SAID OVEN, AND THEN EXTERNALLY APPLYING HEAT TO THE WALLS OF SAID OVEN WHEREBY COKE IS FORMED AND GASES ARE EVOLVED, THE EVOLVED GASES BEING LED OFF THROUGH THE FORMED HOT COKE.

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